Heat radiating members are used in semiconductor elements mounted on various electronic/electrical instruments, such as a computer, other heat generating members, and so on. When a graphite film, out of the heat radiating members, is used for a large-size product, the graphite film is preferably a long and large-area graphite film made from a polymeric film wound into a roll form. Thus, in order to produce this, various investigations have been made.
Suggested is, for example, a method of winding a polymeric film having a width of 250 mm and a length of 30 m around a carbonaceous cylindrical core having an outer diameter of 150 mm, and then subjecting the workpiece to heat treatment. The method makes it possible to yield a long and large-area graphite film about which the cylindrical hysteresis can easily be drawn or stretched (Patent Document 1). However, according to such a conventional method, a large sagging Zgs is unfavorably generated as shown in FIG. 1. It is impossible to restrain this sagging to produce a graphite film excellent in flatness. In such a conventional graphite film, a defect is easily generated, for example, when the film is laminated onto another sheet (see FIG. 2). Moreover, at the time of winding the graphite film onto a branch tube (see FIG. 3), and other times, an inconvenience may be caused.